The present invention relates to an internal combustion engine system, a method for increasing the temperature in such a system and a vehicle comprising and/or operating such a system.
At current and future emission levels for internal combustion engines in vehicles, particularly for heavy duty diesel engines, aftertreatment of the exhaust gas has increased in importance for both emissions and overall fuel consumption. Also drivability and dependability of the vehicles are affected by the different methods used to fulfill these emission standards.
One of the known methods is the use of a so called exhaust gas aftertreatment system usually in form of a catalyst or particle filter. These catalytic aftertreatment systems are operated within a suitable temperature range, for example 250° C.-450° C. which is easily maintained during normal driving conditions of a vehicle.
However, when cold starting the engine or under certain engine operation modes, the actual temperature is too low for said temperature range to be maintained.
Thus, one of the most challenging tasks for running an internal combustion engine system with an exhaust gas aftertreatment system is to increase and maintain the temperature in the exhaust gas aftertreatment system at a working temperature during temperature critical operation situations, so that the emission requirements may be met.
Besides the cold start situation, when the vehicle is started after the engine has been stopped, there are certain other temperature critical engine operating conditions of an internal combustion engine where the actual exhaust gas temperature is too low for said temperature range to be able to be maintained. These temperature critical operating conditions are hereinafter referred to as “low load, idle or motoring engine operation modes” and are described more in detail in the following paragraphs.
The “idle engine operation condition” describes all engine operation modes, where the engine is running at idle speed. Idle speed is the rotational speed the engine runs on when the engine is decoupled from the drivetrain and the accelerator of the internal combustion engine is released. Usually, the rotational speed is measured in revolutions per minute, or rpm, of the crankshaft of the engine. At idle speed, the engine generates enough power to run reasonably smoothly and operate its ancillary equipment (water pump, alternator, and, if equipped, other accessories such as power steering), but usually not enough to perform heavy work, such as moving the vehicle. For vehicles such as trucks or cars, idle speed is customarily between 600 rpm and 1,000 rpm. Even if the accelerator is released, a certain amount of fuel is injected into the internal combustion engine in order to keep the engine running.
If the engine is operating a large number of accessories, particularly air conditioning, the idle speed must be raised to ensure that the engine generates enough power to run smoothly and operate the accessories. Therefore most engines have an automatic adjustment feature in the carburetor or fuel injection system that raises the idle speed when more power is required.
The “low load or motoring engine operation mode” is defined as an engine operation mode, where the engine is running above a certain rotational speed (rpm), but no fuel is injected into the engine. One example of a motoring engine operation node is when the engine is dragging, i.e. when a vehicle —which is normally driven by the engine—is coasting down a hill. During that mode the accelerator is also released, but the engine remains coupled to the drivetrain and the engine is kept running by the drive force of the gearbox main shaft.
During the above described engine operation modes, the engine is in principle pumping fresh air at ambient temperature to the exhaust system, whereby, disadvantageously, the exhaust gas aftertreatment system is “air cooled” in an uncontrolled (and unwanted) manner.
This in turn means that the temperature in the catalytic exhaust gas aftertreatment system drops rapidly below 250° C., so that an effective exhaust gas aftertreatment cannot be provided any more.
Increased emission control requirements have therefore often resulted in a loss of efficiency of the internal combustion engine. It is therefore important to provide methods which allow effective exhaust emission control without adversely affecting the efficiency of the engine and the overall fuel consumption of the vehicle.
Another approach for providing an efficient internal combustion engine with the required low emission is using the so called partial premixed combustion (PPC). PPC can simplified be described as running a compression ignition engine on fuel with a low cetane number e.g. on naphtha or kerosene. The low cetane fuel works fine at medium or high load but the combustion quality is not acceptable at low loads idle and/or motoring engine operation modes. Therefore PPC can also be regarded as provoking a temperature critical operation situation, particularly, during cold start, idle and low load driving situations, when a problem with excessive hydrocarbon compounds (HC) and carbon monoxide (CO) engine emissions occurs.
As mentioned above, HC and CO emission is not a problem if the exhaust gas aftertreatment system is active. But the conversion efficiency drops to unacceptable levels when the catalyst temperature drops below 250° C. Consequently it is required to maintain the temperature of the exhaust gas aftertreatment system at temperatures above 250° C. even at low loads or during idle or motoring engine operation modes and/or to heat up the exhaust gas aftertreatment system rapidly.
It is therefore desirable to provide an internal combustion engine system and a method for controlling an internal combustion engine system, with which the temperature in the exhaust gas aftertreatment system may be increased to a working temperature rapidly and/or maintained in a working temperature range for a long time.
According to a first aspect of the invention, the object is solved by an internal combustion engine comprising a cylinder block with a plurality of cylinders, a gas intake manifold for providing at least air to the cylinder block and an exhaust gas manifold for exiting the exhaust gas from the cylinder block. The exhaust gas manifold comprises at least a main exhaust gas outlet and a waste gate exhaust gas outlet, wherein the main exhaust gas outlet is connected to a main exhaust gas pipe for guiding the exhaust gas to a main exhaust gas aftertreatment system and the waste gate exhaust gas outlet is connected to a waste gate exhaust gas pipe. Inventively, the waste gate exhaust gas pipe is reconnected to the main exhaust gas pipe upstream of the main exhaust gas aftertreatment system and comprises at least one waste gate exhaust gas aftertreatment unit, preferably an oxidation catalyst such as a diesel oxidation catalyst, for catalytically treating the exhaust gas streaming through the waste gate exhaust gas pipe. The main exhaust as aftertreatment system may comprises at least one of the group comprising an oxidation catalyst, a particulate filter, and a selective catalytic reduction reactor.
The waste gate exhaust gas aftertreatment unit, particularly the diesel oxidation catalyst (DOC) or any other suitable exhaust gas aftertreatment unit uses O2 (oxygen) in the exhaust gas stream to convert CO (carbon monoxide) to CO2 (carbon dioxide) and HC (hydrocarbons) to H2O (water) and CO2. This conversion process is exothermic and therefore produces sufficient heat which in turn increases the temperature of the overall exhaust gas, so that a main exhaust gas aftertreatment system arranged downstream of the reconnection of main exhaust gas pipe and waste gate exhaust gas pipe may be maintained at or brought to its the working temperature, preferably a temperature above 250° C. The resulting temperature may additionally be controlled by the amount of exhaust gas streaming through the waste gate exhaust gas pipe, which in turn may be controlled by a waste gate exhaust gas outlet valve and/or the diameter of the waste gate exhaust gas pipe.
The waste gate exhaust gas aftertreatment unit is further adapted to produce exhaust gas with sufficient heat for initializing the exothermic catalytic reaction in the main oxidation catalyst. For initializing the exothermic reactions in the waste gate oxidation catalyst and/or in the main oxidation catalyst a certain amount of unburned fuel—providing the hydrocarbon source—is necessary.
According to a further preferred embodiment, the waste gate oxidation catalyst and the main oxidation catalyst may be configured to be the same unit. Preferably the integrated oxidation catalyst comprises a first entry which is in connection with the waste gate exhaust gas pipe and a second entry which is in connection with the main exhaust gas pipe. Thereby, the first entry is preferably arranged upstream of the second entry.
According to a further preferred embodiment, the unburned fuel may be provided by a fuel injector arranged in or at the waste gate exhaust gas pipe.
Additionally or alternatively, unburned fuel may be provided by a so called very late post injection, where fuel is injected into at least one cylinder of the cylinder block at the end of the combustion stroke so that the fuel is not ignited. Since very late injection strategies are known for creating oil dilution problems, they should be used only sparingly. However, using this method to kick-start the waste gate aftertreatment unit does not take long and is expected to not create problems with oil dilution. During PPC combustion, which will be described in detail below, this problem does not occur due to the high volatility of the PPC fuel. With PPC there is no need to limit the use of very late post injections for oil dilution reasons.
The very late post injection has the further advantage that a right timing of the very late post injection allows for the fuel being pretreated in the cylinder, whereby the hydrocarbons of the injected fuel are converted to lighter hydrocarbons. CO and H2 (hydrogen). Advantageously, the lighter hydrocarbons are easier to ignite in the oxidation catalyst than the hydrocarbons of the injected fuel. Further, in case the internal combustion engine is controlled to provide sufficient CO at the waste gate aftertreatment unit, the waste gate aftertreatment unit may already ignite around 150° C. For maximizing the production of CO, the air to fuel ratio Lambda may be controlled for providing a corresponding condition in the waste gate exhaust gas pipe, preferably a slightly rich condition.
Lambda (λ) is the ratio of actual air to fuel ratio to the stoichiometric air to fuel ratio for a given mixture. Consequently, Lambda is independent on variations in the fuel mixture, since the composition of common fuels may vary seasonally, and many modern vehicles may handle different fuels. A stoichiometric mixture has just enough air to completely burn the available fuel. Lambda of 1.0 indicates a stoichiometric mixture, rich mixtures are less than 1.0, and lean mixtures are greater than 1.0.
As soon as the waste gate oxidation catalyst is ignited, it is possible to terminate the very late post injection and to operate the internal combustion engine on rich conditions. The rich combustion condition provides enough heat and unburned fuel for initializing operation in the main oxidation catalyst. Further, the rich combustion may pre-treat the fuel to make it easier to ignite. As with the very late post injection, a Lambda is suitable for maximising the production amount of CO and H2 relative to HC. This is a suitable strategy just after the waste gate aftertreatment unit has ignited in order to support ignition of the at least one main exhaust gas aftertreatment unit. When the main exhaust gas aftertreatment unit has been ignited, the conditions in the waste gate exhaust gas pipe may typically be at least slightly rich for heat up of the main exhaust gas aftertreatment unit, rapidly. The preferred steps for cold starting the internal combustion engine will be described in detail later on.
During motoring engine operation conditions, the waste gate exhaust gas pipe and the waste gate exhaust gas aftertreatment unit may be used as so called “pilot flame” for an air cooled exhaust gas aftertreatment system by instantly providing sufficient heat for reinitializing the catalytic reaction in the main exhaust gas aftertreatment system. For restarting the main exhaust gas aftertreatment system also the above and more detailed later on described method may be used.
According to a further embodiment, a turbocharger is arranged at or near the main exhaust gas outlet. The inventive waste gate exhaust gas pipe then works as bypass to a turbocharger. Advantageously, bypassing the turbocharger also increases the heat in the main exhaust gas pipe, since the turbocharger provides a massive thermal inertia which cools down the exhaust gas during idle or motoring engine operation modes or consumes a major amount of thermal energy from the exhaust gas for warming up from at cold start Bypassing the turbocharger provides uncooled exhaust gas to the main exhaust gas aftertreatment system. Using a two stage turbocharger increases the cooling phenomenon, since the low pressure turbine is usually quite big and heavy.
Since the temperature problem only occurs during certain temperature critical situations, it is preferred if the waste gate exhaust gas pipe may further comprises a valve which is adapted to control the amount of exhaust gas streaming through the waste gate exhaust gas pipe, so that during medium or high load engine operation modes, the waste gate exhaust gas pipe may be closed.
According to a further preferred embodiment, the waste gate fuel injector may be used for a burner for increasing the temperature of the exhaust gas in the waste gate exhaust gas pipe, directly. Thereby, the exhaust gas temperature in the waste gate exhaust gas pipe is high enough for increasing the overall temperature of the exhaust gas streaming through the first exhaust gas pipe and the waste gate exhaust gas pipe.
According to a further preferred embodiment, the fuel injector and/or the at least one exhaust gas aftertreatment unit are in close vicinity to the exhaust gas manifold for capturing the pulse energy of the exhaust pulse. The pulse energy may enhance the mixing of the exhaust gas and of the injected fuel.
According to a further preferred embodiment, the plurality of cylinders of the cylinder block is arranged in at least a first cylinder group and a second cylinder group. Preferably, each cylinder group comprises an intake throttle, which is adapted to be separably operable. Optionally, the intake manifold may comprise a first intake manifold part which is assigned to the first cylinder group and a second intake manifold part which is assigned to the second cylinder group. This arrangement enables the internal combustion engine system to be controlled in such a way that during temperature critical engine operation situations, the first cylinder group is not provided with fuel, thereby constituting an inactive cylinder group and that the second cylinder group is provided with fuel, thereby constituting an active cylinder group. The active second cylinder group produces sufficient hot exhaust gas for maintaining the main exhaust gas aftertreatment system in its working temperature range, particularly since the amount of fresh air at ambient temperature is also reduced due to the reduced overall volume of pumped gas of the inactive cylinders.
According, to a further preferred embodiment, the exhaust gas manifold is adapted to provide in the exhaust gas manifold a first exhaust gas flow from the first cylinder group, preferably to the first exhaust gas outlet, and a second exhaust gas flow from the second cylinder group, preferably to the second exhaust gas outlet. Since the exhaust gas from the first cylinder group and the second cylinder group are not mixed in the exhaust gas manifold, but guided to the respective exhaust gas outlets, the temperature in the waste gate exhaust gas pipe may be increased even further since only hot exhaust gas from the active second cylinder group is directed to the waste gate exhaust gas pipe. Particularly during low load engine operation modes, the temperature of the exhaust gas of the active cylinder group is even higher than during operation of all cylinders at low load, since the power provided by all cylinders is now provided only by the active cylinder group. This in turn means that the load in the active cylinder group needs to be increased from low load to medium or even high load, which in turn increases the temperature of the exhaust gas of the active cylinder group.
According to a further preferred embodiment, the exhaust gas flow separation may be achieved by providing a separation element in the exhaust gas manifold, so that the exhaust gas manifold is adapted to provide a first exhaust gas manifold part which is assigned to the first exhaust gas outlet and a second exhaust gas manifold part which is assigned to the second exhaust gas outlet.
According to a further preferred embodiment, the exhaust gas manifold is further adapted to provide a third exhaust gas flow through a third exhaust gas pipe, wherein the third exhaust gas pipe is preferably assigned to the second exhaust gas manifold part. Further, the third exhaust gas pipe is adapted to provide exhaust gas to at least one turbocharger unit. Preferably, the first and the third exhaust gas pipe may be adapted to provide exhaust gas to the same turbocharger unit, wherein preferably the turbocharger unit comprises a dual entry turbine. The use of a dual entry turbine reduces the overall components in a vehicle and thereby reduces the overall weight which in turn reduces fuel consumption and increases the vehicle payload possibility. Additionally, a dual entry turbine increases the turbine efficiency since smaller turbocharger components always have lower efficiencies.
According to a further preferred embodiment, the internal combustion engine system further comprises an exhaust gas recirculation (EGR) system for recirculating at least part of the exhaust gas to the gas intake side of the internal combustion engine, wherein preferably the exhaust gas is branched off directly from the exhaust gas manifold or is branched of from the main and/or third exhaust gas pipe downstream of a turbocharger unit and preferably upstream of at least one unit of the main exhaust gas aftertreatment system, particularly upstream of a selective reduction reactor but preferably downstream of a particle filter unit for recirculating filtered exhaust gas.
Advantageously, the EGR reduces the emission of the combustion engine, particularly the quantity of nitrogen oxide in the exhaust gases. Preferably, the recirculated sub-flow of exhaust gas is cooled before fed into the gas intake side of the EGR engine, where it is mixed with incoming air before the mixture is introduced into the cylinders of the EGR engine. Cooling of the recirculated exhaust gas is a prerequisite for the EGR engines as recirculating hot exhaust gas would increase the temperature of the gas at the gas intake side of the EGR engine to a level which could damage the EGR engine. Moreover, recirculation of exhaust gas amounts in a wide range of 10% to 90%, dependent on e.g. engine load and engine operation mode of the total mass flow through the EGR engine is required for yielding a sufficient NOx reduction, According to a further preferred embodiment, the internal combustion engine system further comprises an exhaust gas recirculation duct, which is branched off from the main exhaust gas manifold part which is assigned to the first inactive cylinder group and is adapted to recirculate exhaust gas to the intake manifold, preferably to the second intake manifold part which is assigned to the second active cylinder group. This arrangement advantageously forces exhaust gas from the inactive cylinder group, which is more or less air under the regarded circumstances, to flow from the exhaust gas manifold of the inactive cylinder group to the intake manifold of the active cylinder group so that the overall amount of air flow through the engine is significantly reduced. Thereby the air cooling effect during temperature critical engine operation modes may be further reduced.
According to a further preferred embodiment, the internal combustion engine is adapted to be operated by a less ignitable fuel, particularly by a fuel having a low octane number such as a cetane number below 38 and/or is adapted to ignite the fuel at a compression ratio in the range between 10:1 and 30:1, preferably between 13:1 and 25:1, and most preferably between 15:1 and 18:1. As mentioned above, running an engine by less ignitable fuel creating, so called partial premixed combustion (PPC), also provokes temperature critical situation, particularly during low load or idle engine operation modes. The above described inventive features of the internal combustion engine system allow for an increased, temperature in the cylinders and/or the exhaust gas and may be also used for PPC engines.
A further aspect of the present invention regards methods for controlling an internal combustion engine system, so that the temperature in at least one part of the internal combustion engine system is increased during a temperature critical operation situation such as running the internal combustion engine with less ignitable fuel, and/or a cold start situation and/or a low load engine operation mode and/or an idle engine operation mode and/or a motoring engine operation mode. As mentioned above, the internal combustion engine may comprise a cylinder block with a plurality of cylinders, wherein the plurality of cylinders of the cylinder block are arranged in at least a first cylinder group and a second cylinder group, a gas intake manifold for providing at least air to the first and second cylinder group and an exhaust gas manifold for exiting the exhaust gas from the cylinder block to a main exhaust gas aftertreatment system.
According to a first aspect of the present invention, a preferred embodiment of the method comprises the steps of: Determining whether the internal combustion engine system is operated in the temperature critical situation; and, in case the internal combustion engine system is operated in the temperature critical situation, controlling the first cylinder group to be inactive by providing no fuel to the cylinders of the first cylinder group, and controlling the second cylinder group to be active by providing fuel to the cylinders of the second cylinder group.
Advantageously, instead of pumping fresh air at ambient temperature through all cylinders and thereby cooling the whole internal combustion engine system below its working temperature range during temperature critical operation modes, fresh air is only pumped through part of the cylinders, whereby the amount of fresh air is reduced. Additionally, operating the remaining part of the cylinder with fuel provides hot exhaust gas, but does not increase the fuel consumption unduly. Preferably, the number of cylinders is divided evenly into half, but any other division s also possible.
According to a further preferred embodiment of the inventive method, each cylinder of the internal combustion engine system further comprises at least one intake valve for opening the corresponding cylinder to the intake manifold, and at least one exhaust valve for opening the corresponding, cylinder to the exhaust manifold, the method further comprising the step of increasing the temperature in at least one cylinder by controlling the exhaust valve of the at least one cylinder to be at least partially open at the same time as the intake valve is opened, thereby rebreathing a predetermined amount of exhaust gas into the cylinder.
Advantageously, the rebreathing of the exhaust gas will reduce the air mass flow which in turn increases the temperature of the exhaust gas system. Additionally, the fuel penalty is low.
Preferably, the rebreathing is not performed on all cylinders, but only on the first cylinder group of inactive cylinders, which increases the temperature in the inactive cylinders and therefore also in the exhaust gas. The rebreathing mechanism may be achieved by e.g. an additional cam lobe and/or by a cam phaser in case the internal combustion engine has a separate exhaust cam.
According to a further preferred embodiment at least one cylinder or at least one cylinder group of the internal combustion engine system further comprises an intake throttle for controlling the amount of intake gas into the at least one cylinder or the at least one cylinder group, the method further comprising the step of reducing the amount of intake gas into the inactive cylinder group, wherein preferably the amount of intake gas is almost zero or zero. Thereby, intake of fresh air may be reduced to a much greater extend without over-throttling the engine. Excessive throttling of the engine without exhaust rebreathing would create an underpressure that sucks oil into the cylinder combustion chamber from the sump
According, to a further aspect of the invention relates to a method for increasing the temperature in an internal combustion engine system during a temperature critical operation situation such as running the internal combustion engine with less ignitable fuel, and/or a cold start situation and/or a low load engine operation mode and/or an idle engine operation mode and/or a motoring engine operation mode, wherein the internal combustion engine comprises a cylinder block with a plurality of cylinders, a gas intake manifold for providing at least air to the first and second cylinder group and an exhaust gas manifold for exiting the exhaust gas from the cylinder block. The exhaust gas manifold comprises at least a main exhaust gas outlet and a waste gate exhaust gas outlet, wherein the main exhaust gas outlet is connected to a main exhaust gas pipe for guiding the exhaust gas to a main exhaust gas aftertreatment system and the waste gate exhaust gas outlet is connected to a waste gate exhaust gas pipe, wherein the waste gate exhaust gas pipe is reconnected to the main exhaust gas pipe upstream of the main exhaust gas aftertreatment system and comprises at least one waste gate exhaust gas aftertreatment unit, preferably an oxidation catalyst such as a diesel oxidation catalyst, for catalytically treating the exhaust gas streaming through the waste gate exhaust gas pipe. Inventively, the method comprises the steps of: Determining whether the internal combustion engine is operated in the temperature critical situation; and in case the internal combustion engine is operated in the temperature critical situation opening the waste gate exhaust gas pipe and operating the at least one waste gate exhaust gas aftertreatment unit waste gate exhaust gas pipe.
As mentioned above, the waste gate exhaust gas aftertreatment unit, particularly the diesel oxidation catalyst (DOC) or any other suitable exhaust gas aftertreatment unit uses O2 (oxygen) in the exhaust gas stream to convert CO (carbon monoxide) to CO2 (carbon dioxide) and HC (hydrocarbons) to H2O (water) and CO2. This conversion process is exothermic and therefore produces sufficient heat which in turn increases the temperature of the overall exhaust gas, so that a main exhaust gas aftertreatment system arranged downstream of the reconnection of main exhaust gas pipe and waste gate exhaust gas pipe may be maintained at or brought to its the working temperature, preferably a temperature above 250° C.
As also mentioned above, the waste gate exhaust gas pipe provides a bypass to a turbine of a turbocharger or at least a turbocharger unit which may be arranged in the main exhaust gas pipe. Since the exhaust gas streaming through the waste gate exhaust gas pipe is not used for beating the turbocharger, the overall heat of the exhaust gas may be increased. Additionally a fuel injector or a so called very late post injection may be used as hydrocarbon source for the waste gate exhaust gas aftertreatment unit.
Preferably, the main exhaust gas outlet is assigned to a first cylinder group, and the waste gate exhaust gas outlet and the optional third exhaust gas outlet are arranged at a second cylinder group, wherein the main and preferably the third exhaust gas outlet are connected to the first exhaust gas pipe and the waste gate exhaust gas outlet is connected to the waste gate exhaust gas pipe.
According to a further preferred embodiment of the inventive method, at least one step of the above described rebreathing and at least one step of bypassing the turbocharger by means of the waste gate exhaust gas pipe are performed. This minimizes the amount of cold air flowing through the internal combustion engine system and therefore increases the temperature in the exhaust gas.
Preferably, the exhaust rebreathing is performed on the first cylinder group of inactive cylinders. Advantageously, this avoids pumping back exhaust gases through the waste gate exhaust gas pipe.
According to a further preferred embodiment, each cylinder may comprise a cylinder fuel injector for injecting at least fuel into the cylinders, wherein the cylinder fuel injector of at least one cylinder, preferably of at least one cylinder of the second active cylinder group, is controlled to inject fuel at at least two times per combustion stroke, wherein preferably the second injection is significantly later than the first injection, preferably at least 10 crank angle degrees later than the first injection, most preferably at least 20 crank angle degrees later than the first injection.
This so called late post injection has the advantage that instead of injecting the whole amount of fuel at one time, the fuel amount is split into at least two injections, wherein the second injection is significantly later than the first injection, which increases the exhaust gas temperature. However care should be taken that a too late second injection may have the consequence that the fuel does not ignite. This might be wanted for adjusting the air to fuel ratio and is called very late post injection in this document—see above. The second injection advantageously increases the temperature to the exhaust gases by boosting the temperature rapidly and for a short period of time so that the fuel penalty is acceptable.
It goes without saying, that also a very late post injection as described above may be performed for generating CO and H2 and igniting the oxidation catalyst(s) at low temperature, preferably at a temperature around 150° C.
According to a preferred embodiment, an inventive cold starting process (or process performed after a long period of idle engine operation modes) comprises the following steps:    1. Operating the second cylinder group with late post injection    2. When the temperature of the exhaust gas in the waste gate exhaust gas pipe or at the waste gate exhaust gas aftertreatment unit has been reached roughly 150° C., operating the second cylinder group with a very late post injection for producing CO and H2, preferably using a suitable an to fuel ratio for maximizing the CO and H2 content in the exhaust gas.    3. Initializing operation (igniting) of the waste gate exhaust gas aftertreatment unit at roughly 150° C. due to the presence of CO and H2 in the exhaust gas of the waste gate exhaust gas pipe.    4. Terminating very late post injection and initializing operation of the waste gate fuel injector.    5. Maintaining thereby conditions in the waste gate exhaust gas pipe close to a stoichiometric mixture of fuel and air for initializing operation of the main exhaust gas aftertreatment system at roughly 150° C. due to the presence of CO and H2.    6. After ignition of the main exhaust gas aftertreatment system, increasing the fuel amount at the waste gate fuel injector for providing at least slightly rich, preferably rich conditions in the waste gate exhaust gas pipe for providing unburned fuel to the main oxidation catalyst, which in turn result in rapid heating of the main exhaust gas aftertreatment system.    7. Optionally, operating the first cylinder group for providing sufficient power if required.
According to a further preferred embodiment, the first cylinder group comprises at least one first intake throttle, and the second cylinder group comprises at least one second intake throttle, which are adapted to be separably operable, the method further comprising the step of: during the temperature critical situation controlling the first intake throttle of the first cylinder group and the second intake throttle of the second cylinder group to throttle the first cylinders of the first cylinder group to a greater extent than the second cylinders of the second cylinder group.
Throttling the air intake, particularly to the first cylinder group of inactive cylinders reduces the overall amount of fresh air being pumped through the cylinders. Particularly advantageous is the combination of at least one step of the exhaust rebreathing method and the step of intake throttling, as it provides powerful flow control and reduces the amount of fresh air in the internal combustion engine system, significantly. Thereby, the temperature of the exhaust gas may be increased.
According to a further preferred embodiment, the inventive method may further comprise the step of recirculating at least part of the exhaust gas to the gas intake side of the internal combustion engine, wherein the internal combustion engine system further comprises an exhaust gas recirculation (EGR) system for recirculating at least part of the exhaust gas to the gas intake side of the internal combustion engine, wherein preferably the exhaust gas is branched off from the main and/or third exhaust gas pipe downstream of a turbocharger unit and preferably upstream of the main exhaust gas aftertreatment system, or is branched off directly from the exhaust as manifold.
Recirculating at least part of the exhaust gas during temperature critical situations may increase the temperature of the exhaust gas since the intake of fresh air may be reduced. The warm exhaust gas streams through the cylinders and subsequently through the exhaust gas and avoids cooling down of the internal combustion engine system and particularly of the exhaust gas aftertreatment system.
According to a further aspect, the invention relates to a method for increasing the temperature in an internal combustion engine system during a temperature critical operation situation such as running the internal combustion engine with less ignitable fuel, and/or a cold start situation low load engine operation mode and/or an idle engine operation mode and/or a motoring engine operation mode, wherein the internal combustion engine system comprises a cylinder block with a plurality of cylinders, wherein the plurality of cylinders of the cylinder block are arranged in at least a first cylinder group and a second cylinder group, a first gas intake manifold part which is assigned to the first cylinder group for providing at least air to the first cylinder group, a second gas intake manifold part, which is assigned to the second cylinder group for providing at least air to the second cylinder group, a first exhaust gas manifold part for exiting exhaust gas from the first cylinder group, a second exhaust gas manifold part for exiting exhaust gas from the second cylinder group, and an exhaust gas recirculation duct, which connects the first exhaust gas manifold part and the second gas intake manifold part of the internal combustion engine. The inventive method comprises the steps of: Determining whether the internal combustion engine is operated in the temperature critical situation; and in case the internal combustion engine is operated in the temperature critical situation recirculating exhaust gas from the first cylinder group to the second cylinder group.
Preferably, the method further comprises the step of controlling the first cylinder group to be inactive by providing no fuel to the cylinders of the first cylinder group, and controlling the second cylinder group to be active by providing fuel to the cylinders of the second cylinder group in case the internal combustion engine system is operated in the temperature critical situation.
Due to the exhaust gas recirculation from the exhaust gas manifold of the inactive (first) cylinder group to the intake manifold for the active (second) cylinder group, air is forced to flow from the first inactive exhaust manifold part to the second active intake manifold part. Additionally throttling the air intake upstream on the active intake manifold, will increase the forced air flow. Consequently, fresh air passes first to the inactive cylinder group and is then fed to the active cylinder group, thereby passing the internal combustion engine twice. Hence, the overall amount of air flowing through the internal combustion engine may be reduced significantly.
This method has the advantage that rebreathing of exhaust gas does not need to be performed for increasing the exhaust gas temperature. Additionally, the problem of accumulation of soot from pulsating EGR with following bad distribution is avoided since the reused air does not necessarily be mixed with recirculated exhaust gas.
Further, by using the above described engine operation method, provides a further method for providing pre-treated fuel. In this case, the fuel may be post injected lately into the first inactive cylinder group and, provided the injection timing is right, the pre-treated fuel enters then the active cylinders with increased ignitability.
According to a further preferred embodiment, the above described use of pre-treated fuel may also be achieved by using the exhaust rebreathing in combination with exhaust gas recirculation to the active cylinder group. Provided the exhaust rebreathing is performed on the inactive cylinders and not on the active cylinders and there is a common exhaust gas manifold and a common intake manifold for both cylinder groups, exhaust gas from the active cylinder group may be rebreathed by the inactive cylinder group from the exhaust gas manifold. A rightly timed very late post injection may then provide pre-treated fuel which in turn is provided to the intake manifold of the active cylinder group as fuel with increased ignitability.
It goes without saying that according to further embodiments, also this method may be combined with the above, described steps of the bypass method and/or of the rebreathing method. Particularly by combining the bypass method and the method of the reused air, thermal inertia at cold starting may be reduced.
Even if not each and every combination possibility of the method steps and/or system features has been mentioned in detail above, it is clear for a person skilled in the art that the features and steps ma be combined in any suitable manner without being inventive.
Further preferred embodiments and advantages are defined in the claims, the figures and the description.
In the following same or similarly functioning elements are indicated with the same reference numerals.